/Engine/Source/Runtime/GeometryCore/Public/DynamicMeshEditor.h
Find "new" color for input color element underIndexmapping, or create new if missing
index of duplicate color in given color layer
int FindOrCreateDuplicateColor ( int ElementID, [FMeshIndexMappings](API\Runtime\GeometryCore\DynamicMesh\FMeshIndexMappings) & IndexMaps, [FDynamicMeshEditResult](API\Runtime\GeometryCore\FDynamicMeshEditResult) * ResultOut )